1. Field of the Invention
This invention relates to a stitch data preparing device for an embroidery sewing machine, and more particularly to a stitch data preparing device which freely sets the shape of an embroidery area in which embroidery stitches are formed, and forms embroidery stitches which properly reflect the shape of the embroidery area.
2. Description of Related Art
In Japanese Patent Publication No. 60-42740, for example, a conventional embroidery pattern storing and reproducing device is described which stores embroidery data for effecting embroidery stitching in a very small capacity memory. In this embroidery pattern storing and reproducing device, an embroidery zone such as a character or a figure is divided into a plurality of blocks. The embroidery area data, including block data defining an outline of each block and thread density data defining the number of stitches to be formed in each block by an embroidery thread, is also stored. Then, position data of the needle locations in each block is obtained based on the block data and the thread density data. Embroidery stitches are formed by a sewing machine using the position data of the needle locations.
In using the embroidery pattern storing and reproducing device to prepare the embroidery data, the embroidery zone is divided into a plurality of rectangular blocks. As shown in FIG. 30, in preparing embroidery area data for an embroidery zone 100 shaped, for example, like a leaf of a plant. A left half portion of the embroidery zone 100 is divided into three blocks B1, B2 and B3. A right half portion of the embroidery zone 100 is divided into an additional three blocks B4, B5 and B6. Then, the embroidery area data is created from the block data and the thread density data of the six blocks B1 to B6.
The block data of the block B1 comprises coordinates of four end points b11, b12, b13 and b14. The four end points define four outline segments L1, L2, L3 and L4 form the outline of the rectangular block B1. In other words, the block B1 is defined by a pair of first and second main line segments L1 and L2, which are opposed to each other and by a pair of first and second subline segments L3 and L4 connecting the first and second main lines L1 and L2 at each end. A plurality of needle locations are defined on the first and second main lines L1 and L2. In dividing an embroidery zone into a plurality of blocks, the number of divisions of the embroidery zone and the positions of divisions are generally determined based on the shape of the embroidery zone, so that a first subline and a second subline of a first block are generally straight line segments when the first block adjoins a second block.
Thus, an embroidery zone is divided into a plurality of rectangular blocks with the first and second sublines defined as straight line segments. The embroidery area data of each block is then created. Then, the stitch data defining the needle locations on the first and second main lines of each block is generated from the embroidery area data. FIG. 30 shows embroidery stitches formed according to the stitch data of the embroidery zone 200.
However, as the pair of sublines of each block are defined as straight line segments when preparing the embroidery area data, the shape of the block cannot be freely defined. Accordingly, in characters, symbols (including logos and marks) and figures (including animals, flowers, articles, etc.) having a complex shape including a curved portion or a sharply bent portion, the curved or sharply bent portion must be divided into many small blocks, in order to form the sublines as straight line segments. Accordingly, the number of blocks forming the entire embroidery zone is greatly increased, resulting in an increased quantity of the embroidery area data. In addition, creating the embroidery area data becomes vastly more complex.
Embroidery stitches are formed in each block. When the embroidery zone is divided into many small blocks, the shape of the embroidery zone cannot be properly reflected. That is, embroidery stitches along the shapes of the main lines and the sublines cannot be formed. In the arrangement of the six blocks B1 to B6 of the embroidery zone 200, as shown in FIG. 30, including adjacent blocks such as B1 and B4 or B2 and B5, the embroidery stitches are formed independently in these adjacent blocks. Accordingly, undesired spaces arise in the embroidery stitches between adjacent blocks, reducing the quality of the finished embroidery stitch pattern.